Vehicle suspension characteristics generally determine ride height, spring rates, caster, camber, toe-in, braking dive, acceleration squat, and cornering roll. Anti-roll suspension systems are those in which forces that tend to cause roll of the vehicle body with respect to the wheels about a longitudinal axis are resisted by forces acting through or on the suspension system. Vehicle suspension systems having anti-roll characteristics are generally either `active` suspensions using hydraulic actuators to adjust suspension characteristics in response to sensed lateral acceleration, or more commonly, suspensions that incorporate devices such as anti-roll or stabilizer bars that have fixed suspension characteristics.
Typical of an `active` suspension system is U.S. Pat. No. 4,865,347 for Actively Controlled Suspension System Anti-Roll Control, issued to Fukushima et. al. on Sep. 12, 1989, which describes a suspension system having an anti-roll control loop in which the gain is adjusted depending on the speed of the vehicle. The '347 suspension system utilizes acceleration sensors to detect lateral acceleration and pressure control valves to adjust hydraulic cylinders which vary the suspension characteristics according to the speed of the vehicle.
U.S. Pat. No. 4,948,164 for Actively Controlled Suspension System with Compensation of Delay in Phase in Control System, issued to Hano et. al. on Aug. 14, 1990, describes an actively controlled suspension system which can compensate for phase delay caused in a control system and load condition on the vehicle. The active suspension system described in the '164 patent employs a plurality of acceleration sensors for detecting lateral acceleration. Based on the sensed acceleration, anti-rolling suspension control signals are produced for controlling suspension characteristics of left and right-side suspension systems.
U.S. Pat. No. 5,114,177 for Anti-Rolling Controlling System for Automotive Active Suspension System With Road Friction Dependent Variable Control Characteristics, issued to Fukunaga et al. on May 19, 1992, is directed to an active anti-rolling suspension control system having a means for monitoring road friction conditions and a means for distributing rolling moment between front suspension systems and rear suspension systems.
U.S. Pat. No. 3,820,812 for Vehicle Suspension Systems, issued to Stubbs, et. al. on Jun. 28, 1974, is for an active anti-roll suspension control system for four-wheeled road vehicles that have variable-length hydraulic struts acting in series with the front springs controlled by a control unit sensitive to lateral acceleration. The rear suspension anti-roll system is applied by hydraulic cylinders acting on the rear suspension independently of the rear springs and controlled by the control units for the corresponding front struts.
Active anti-roll suspension systems such as those described above have the disadvantage of being relatively complex and have proved too costly to implement in most vehicles. Anti-roll suspension systems with fixed suspension characteristics, in which the anti-roll damping forces do not vary with speed or direction, are also described in the prior art. U.S. Pat. No. 4,573,702 for Anti-Pitch Suspension, issued to Klem on Mar. 4, 1986, for example, is for a vehicle suspension system designed to utilize lateral movement of the body of the vehicle relative to the wheels in order to control the sway or roll of the vehicle body. The '702 suspension system utilizes springs of various types to create an additional means to increase compression or extension of conventional suspension pieces. The principle of the invention may also be used to control dive during braking or squat during acceleration.
U.S. Pat. No. 5,074,582 for Vehicle Suspension System, issued to Parsons on Dec. 24, 1991, depicts a roll frame pivotally mounted transverse of the vehicle, the roll frame having an arm at either end and a wishbone pivotally supported on each arm. Each wishbone forms part of a linkage for supporting a wheel of the vehicle.
U.S. Pat. No. 4,143,887 for Independent Rear Suspension System, issued to Williams et al. on Mar. 13, 1979, depicts a rear suspension utilizing a torsion bar mounted between oppositely disposed wheel carriers and cooperable with laterally extending control arms for providing roll steer characteristics for the rear wheels.
U.S. Pat. Nos. 5,388,855 and 5,193,843 both entitled Suspension System of a Vehicle and both issued to Yamamoto et al. on Feb. 14, 1996 and Mar. 16, 1993, respectively, are directed to a double pivot type suspension system to allow a wheel located radially inward in relation to a turning circle to be turned more sharply than a wheel located radially outward in relation to the turning circle.
U.S. Pat. No. 5,415,427 for Wheel Suspension System, issued to Sommerer et. al. on May 16, 1995, depicts a suspension system comprising a wheel carrier supported on the body side by way of a spring strut. The wheel carrier is guided by two individual links forming an upper pivotal connection and a lower pivotal connection between the wheel and the vehicle body. The pivotal connections are arranged at different angles with respect to the wheel contact plane and, viewed from the top, are arranged to be crossed with respect to one another.
U.S. Pat. No. 4,406,479 for Vehicle Suspension Incorporating Cross-Over Links, issued to Chalmers on Sep. 27, 1983, is directed to a suspension system for a vehicle having a pair of torque rods splayed or outwardly angled relative to the longitudinal axis of the vehicle in which the torque rods cross each other as viewed from the top and are flexibly connected to the vehicle chassis at their inner ends.
Although springs and anti-roll bars described in the prior art reduce cornering roll, there is a trade-off between reduction in roll and the smoothness of the ride. Spring and shock rates that increase the smoothness of the ride counteract the effect of the conventional anti-roll devices described in the prior art. Moreover, such anti-roll devices do not compensate for variations in weight distribution of the vehicle which can also significantly affect rolling characteristics.